Senin, 04 Juni 2012

Natural Rubber Production

The annual worldwide natural rubber production is estimated to be close to 8,800,000 tons (http://www.rubberstudy.com/statistics-quarstat.aspx), almost all of it from one biological source: the Brazilian rubber tree (Hevea brasiliensis). Malaysia, Indonesia, and Thailand together produce nearly 80% of the world supply (Table 1).The yield of rubber varies from 500 kg ha-1 y-1 in smallholder plots to more than 1500 kg ha-1 y-1 in large plantations (Balsiger et al., 2000).

In experimental plots with new Hevea lines, yields of up to 3000 kg ha-1 y-1 have been obtained. Natural rubber from H. Brasiliensis mainly consists of cis-1,4-polyisoprene, with many minor additional components that are key to the superior properties of this material compared to all synthetic rubbers.

The rubber molecules are produced from isoprenoid precursors that are thought to be synthesised as part of the general mevalonic acid (MVA) pathway. A rubber transferase (EC 2.5.1.20) located in the cytoplasm of plant laticifer cells progressively adds isopentenyl-diphosphate moieties onto a single allylic diphosphate primer molecule to form the rubber biopolymer.

The rubber molecules accumulate in particles that are surrounded by a species-specific fatty acid monolayer and rubber particle-associated proteins. The length of the rubber molecules is one of the main determinants for the functional properties of the resulting natural rubber. For an overview of the biochemistry and mechanism of rubber biosynthesis, please consult (Cornish, 2001) and (Puskas et al., 2006).